One important component of a surgical cannula is the tip, disposed on the distal end of the cannula. A properly configured tip can provide important functionality to a cannula. For example, the functions of vessel dissection and transection are commonly performed by two separate instruments. The device described in the pending application Ser. No. 08/907,691, entitled “Tissue Separation Cannula with Dissection Probe and Method,” filed on Aug. 8, 1997, discloses a device for separating surrounding connective tissue from a vessel (dissection). The device described in the pending application Ser. No. 09/102,723, entitled Vessel Isolating Retractor Cannula and Method,” filed on Jun. 22, 1998, discloses a device for retracting the vessel, ligating side branches, and transecting the branches to allow removal of the vessel. It is desirable to use a single device for performing the above functions.
The construction of a cannula tip also affects the visual field provided to a surgeon through an endoscope. When an endoscope is situated in a lumen of the cannula, the surgeon looks through the endoscope and through the transparent tip to view the surgical site. It is desirable to have a tip which maximizes the visual field of the endoscope.
The cannula tip may also be used to dilate a tunnel or anatomical space through tissue planes. In pending application Ser. No. 09/133,136, entitled “TISSUE DISSECTOR APPARATUS AND METHOD,” filed Aug. 12, 1998, assigned to the same assignee as the present application, and which is hereby incorporated by reference, a cannula is constructed with a bulbous element near the tip of the cannula for performing tissue dilation as the cannula is advanced. Cannula tips for dilating tunnels through tissue require force in order to advance the cannula and dilate the tissue. It is desirable to have a tip which can perform tissue dilation or dissection using a minimal amount of force and causing minimal trauma.